It is well known that battery packs that provide power to portable, battery-operated power tools have the drawback of short battery life, especially when the power tool is used often or is heavily loaded. Consequently, users of such power tools are often required to replace a discharged battery pack for either a new battery pack or a recharged battery pack. Such battery packs are relatively expensive to purchase and require a fair amount of time to recharge. Further, rechargers for such battery packs are also fairly expensive.
Welch, in his U.S. Pat. No. 5,076,805 issued on Dec. 31, 1991, recognized the inherent drawbacks with such battery-operated tools. Welch teaches an adapter that replaces the battery pack of such tools and connects to a vehicle battery with a pair of power cables. No provision is made in the Welch device, however, for protectively insulating the electrodes of the device when the device is removed from the battery compartment of the power tool. If such a device is removed from the power tool and inadvertently placed in, for example, a tool box, the electrical contacts can short circuit. Such an occurrence could cause considerable damage to the vehicle battery, especially since, as disclosed, the Welch device connects directly to the battery leads without any intervening fuse means. If in an environment with explosive fumes, a spark caused by such shorting of the electrical contacts can ignite such fumes inadvertently. Further, no provision is made in the Welch device for assuring the correct battery polarity when the device is inserted into the power tool. Depending upon the type of power tool used, a reversed battery polarity can cause the power tool to function incorrectly. Moreover, the connector described in the Welch device is awkward to use, since one must expose the vehicle battery leads, typically by lifting the hood of the vehicle, during use.
Clearly, then, there is a need for an interconnecting power adapter for a power tool that protects and insulates its electrical contacts when not engaged with a power tool. Such a needed device would ensure proper battery polarity when inserted into the power tool, and would have an improved vehicle battery connector means. Further, such a needed device would be relatively inexpensive to manufacture and assemble, allowing for a press-fit assembly of relatively few components. The present invention fulfills these needs and provides further related advantages.